Embodiments of the disclosed technology relate to a light emitting diode package unit, a method for manufacturing the same and a backlight.
Nowadays, light emitting diodes (LEDs), due to low power consumption, long service life, high response speed and so on, are widely used. For example, a light emitting diode backlight in a liquid crystal display (LCD) is shown in FIG. 1. A plurality of LED package units 13 are disposed on a circuit board 12 at one side of a light guide plate 11. Each LED package unit 13 illuminates a local area on the edge of the light guide plate 11. Each LED package unit 13 comprises a light extraction cup 16, a LED chip 15 on the bottom of the light extraction cup 16, and a bar type package element 14 used to package the LED chip 15 in the light extraction cup 16, as shown in FIG. 2 and FIG. 3. Typically, the package element 14 is formed of epoxy resin, which may further contain fluorescent particles in different colors for mixing monochromatic light emitted from the LED package units into white light.
The disadvantages of the above described LED package unit structure are given at least as follows. As shown in FIG. 3, which depicts a partial light path view of an LED package unit of a related art, light rays 9 emitted from the LED chip 15 would be diverged when leaving the upper surface of the package element 14, since the refractive index of the package element 14 is higher that of the surrounding air. The closer the light rays 9 approaches the side parts of the package element 14, the more they deviates from the original optical paths; further, the reflectivity of the light rays becomes larger as the incident angles increase. As a result, the closer the light rays 9 approaches the side parts (i.e., the lager the incident angles are), the more the light rays 9 will be reflected back into the package element 14, and the less the light rays 9 will leave the package element 14. The light rays 9 are totally reflected when the incident angle exceeds the critical angle. In addition, the light rays 9 exiting from the side parts are subject to much energy loss because of long optical paths. As a result, the relative intensity of the exiting light rays 9 from the upper surface of the package element 14 decreases as the exiting angles (i.e., the angles between the light rays 9 exiting from the package element 14 and the vertical directions at the exiting points) increase, as shown in FIG. 4. That is, the intensity of the exiting light rays 9 exiting from the LED package unit 13 is higher in the central part and lower at both side parts, i.e., the intensity is nonuniform. As a result, the uniformity of the light emitted from the backlight is deteriorated. Although regions corresponding to the side parts of one LED package unit 13 may be irradiated by two LED package units 13, the relative intensity is still decreased to 0.4 when the exiting angle is 60°, as shown in FIG. 4. In other words, the relative intensity at the side parts can not reach the same level as that in the central parts, even though superposition of illumination occurs.